Vascular filters are used for effective filtration of blood particularly in the inferior vena cava in order to prevent pulmonary thromboembolism. A need for these filters arises in trauma patients, orthopedic surgery patients, neurosurgery patients, or in patients having medical conditions requiring bed rest or non-movement, as these medical conditions present a possibility of thrombosis in the peripheral vasculature of patients wherein thrombi break away from the vessel wall, risking downstream embolism or embolization. For example, depending on the size, such thrombi pose a serious risk of pulmonary embolism wherein blood clots migrate from the peripheral vasculature through the heart and into the lungs.
A filtering device can be deployed in the vena cava of a patient when, for example, anticoagulant therapy is contraindicated or has failed. Typically, filtering devices are permanent implants, each of which remains implanted in the patient for life, even though the condition or medical problem that required the device has passed. However, designs for removable filters have been provided, such as U.S. Pat. No. 7,763,045 to Osborne and U.S. Pat. No. 7,625,390 to Hendriksen et al.
Filters typically have a conical design provided with a hook on a top surface for accurate placement in the vena cava. A filter is introduced into a patient using a standard percutaneous technique. If a patient's risk of thromboembolism diminishes, the patient no longer requires a filter and the filter can be removed.
A known retrieval device comprises a snare, shaped as a loop, which is used to catch a removal hook on the top of the filter. Unfortunately, filters can become off-centered or tilted with respect to the hub of the filter and the longitudinal axis of the vessel in which it has been inserted, resulting in the removal hook lying close to or against the vessel wall. This can make snaring the removal hook with a retrieval device difficult if not impossible. Additionally, in the event of this occurrence, there is a greater likelihood of endotheliosis of the filter to the blood vessel along a substantial length of the filter wire and/or the retrieval hook. As a result, the filter can become a permanent implant in a shorter time period than otherwise. It is also possible that, in some patients, the hook on the filter becomes calcified, thus inhibiting retrieval of the filter. Thus, there is a need for alternative devices and methods for retrieving vascular filters implanted in patients.